Check if int is between two numbers

Why can't do you this if you try to find out whether an int is between to numbers:

if(10 < x < 20)

Instead of it开发者_高级运维, you'll have to do

if(10<x && x<20)

which seems like a bit of overhead.

One problem is that a ternary relational construct would introduce serious parser problems:

<expr> ::= <expr> <rel-op> <expr> |
           ... |
           <expr> <rel-op> <expr> <rel-op> <expr>

When you try to express a grammar with those productions using a typical PGS, you'll find that there is a shift-reduce conflict at the point of the first <rel-op>. The parse needs to lookahead an arbitrary number of symbols to see if there is a second <rel-op> before it can decide whether the binary or ternary form has been used. In this case, you could not simply ignore the conflict because that would result in incorrect parses.

I'm not saying that this grammar is fatally ambiguous. But I think you'd need a backtracking parser to deal with it correctly. And that is a serious problem for a programming language where fast compilation is a major selling point.

Because that syntax simply isn't defined? Besides, x < y evaluates as a bool, so what does bool < int mean? It isn't really an overhead; besides, you could write a utility method if you really want - isBetween(10,x,20) - I wouldn't myself, but hey...

It's just the syntax. '<' is a binary operation, and most languages don't make it transitive. They could have made it like the way you say, but then somebody would be asking why you can't do other operations in trinary as well. "if (12 < x != 5)"?

Syntax is always a trade-off between complexity, expressiveness and readability. Different language designers make different choices. For instance, SQL has "x BETWEEN y AND z", where x, y, and z can individually or all be columns, constants, or bound variables. And I'm happy to use it in SQL, and I'm equally happy not to worry about why it's not in Java.

You could make your own

public static boolean isBetween(int a, int b, int c) {
    return b > a ? c > a && c < b : c > b && c < a;
}

Edit: sorry checks if c is between a and b

The inconvenience of typing 10 < x && x < 20 is minimal compared to the increase in language complexity if one would allow 10 < x < 20, so the designers of the Java language decided against supporting it.

COBOL allows that (I am sure some other languages do as well). Java inherited most of it's syntax from C which doesn't allow it.

You are human, and therefore you understand what the term "10 < x < 20" suppose to mean. The computer doesn't have this intuition, so it reads it as: "(10 < x) < 20".

For example, if x = 15, it will calculate:

(10 < x) => TRUE

"TRUE < 20" => ???

In C programming, it will be worse, since there are no True\False values. If x = 5, the calculation will be:

10 < x => 0 (the value of False)

0 < 20 => non-0 number (True)

and therefore "10 < 5 < 20" will return True! :S

simplifying:

a = 10; b = 15; c = 20

public static boolean check(int a, int b, int c) {
    return a<=b && b<=c;
}

This checks if b is between a and c

Because the < operator (and most others) are binary operators (they take two arguments), and (true true) is not a valid boolean expression.

The Java language designers could have designed the language to allow syntax like the type you prefer, but (I'm guessing) they decided that it was not worth the more complex parsing rules.

One can use Range class from the Guava library:

 Range.open(10, 20).contains(n)

Apache Commons Lang has a similar class as well.

if (10 < x || x < 20)

This statement will evaluate true for numbers between 10 and 20. This is a rough equivalent to 10 < x < 20